The Contemporary image forming apparatuses are provided with colorless toner or colorless ink, which are collectively referred to as “clear toner”. In addition to a widely known use of clear toner to protect the printed surface or to create glossy effects, clear toner may be used to generate various colorless patterns to add visual variety to the printed image. For example, as described in Japanese Patent Application Publication Nos. 2008-532066 and 2008-145453 (JP-2008-532066-A and JP-2008-145453-A), an operator may apply any desired colorless pattern to any desired portion of the printed image.
However, it has been difficult for a general user to determine which colorless pattern should be applied to which portion of image data to be processed.